The Wilson Journal of Ornithology 124(3):513-517. 2012 
NEST-SITE CHARACTERISTICS AFFECT PROBABILITY OF 
NEST PREDATION OF BULL-HEADED SHRIKES 
SACHIKO ENDO 1: 
ABSTRACT—I investigated the relationship between the probability of nest predation and nest-site characteristics: 1) 
nest heiaht above around. (2) number of branches attached to a nest, and (3) number ot thorny branches around the nest tor 
a population of Bull-headed Shrikes (Lunius bucephalus) breeding in Japan. Thn ty-eight nests were located during 0 
and 2CKW of which 16 were lost to predation. 14 were successful in Hedging young, tour were, abandoned two were 
parasitized, and two may have been partially depredated, although the actual reason is unclear. Ne.ther n^t he.ght nor the 
number of thomv branches was correlated with breeding success. However the number of branches wa negatively 
correlated with probability of nest predation. The primary predators were bch ev ed to be birds, based on physisa 
depredated nests. A high density of branches around nests of Bull-headed Shrikes may ensure they are not easily discovered 
and depredated by predators. Received 26 September 2011. Accepted 4 February 2012. 
Nest predation is the major cause ot breeding 
failure for many bird species (Ricklefs 1969. 
Martin 1993). Nest-site characteristics along with 
nest defense behavior are the most important 
factors related to nest predation (Collins and 
Col lias 1984. Caro 2005). Previous studies have 
reported that features such as extent of nest 
concealment and nest height affect nest predation 
(Caro 2005). For example, greater nest cover 
reduces the probability that a predator will Imd a 
nest (Collias and Collias 1984. Martin and Roper 
1988). Similarly, nest height reduces accessibility 
for some terrestrial predators, which may lind it 
difficult to access elevated nests (Collias and 
Collias 1984). Thus, nest-site characteristics can 
strongly affect the success of many breeding birds. 
Branches supporting a nest may also function to 
reduce predation in shrub-nesting species, as high- 
density branches could conceal a nest. Similarly, 
branch density may also reduce access by 
predators. However, there has been scant inves¬ 
tigation into the predator-deterring effects ot 
branches. In addition, the features ol branches, 
such as those with thorns, may affect access lor 
nest predators. Some species select thorny plants 
for nesting (Lack and Lack 1958. Gawlik and 
Bildstein 1990, Yosef 2001), but the effect of 
thorns is unknown. 
Bull-headed Shrikes (.Lanins bucephahts) build 
an open-cup nest in shrubs or bushes (Yamagishi 
Department of Lite Science, Faculty of Science. 3 olio 
University. Miyama 2-2-1. Hunabashi. Chiba 274-8510. 
Japan. 
: Current address: Department of Life Science, Faculty of 
Sciences. Rikkyo University. Nishi-lkebukuro 3-34-1. 
Toshima, Tokyo 171-8501. Japan: e-mail: 
s.endo@rikkyo.ac.jp 
1981. Takagi and Abe 1996). Their nests on the 
study area were made with twigs, dead herbs, and 
pieces of polyethylene tape. 1 investigated the 
relationship between nest-site characteristics and 
the probability of nest predation by measuring and 
correlating the following variables with nest 
predation: (I) nest height above ground. (2) 
number of branches supporting a nest, and (3) 
number of thorny branches around the nest. 
METHODS 
This study was conducted in the meadowlands 
and cultivated fields at Karuizawa (36 31' N, 
138 59' E: 920 m asl) in Nagano, Japan in 2008 
and 2009. Bull-headed Shrikes in this study area 
begin to nest in early April and continue until late 
July. They are socially monogamous and the 
average dutch size was six eggs (n - 14, range 
= 3_8 eggs). The incubation period was ~ 15 days 
(a — 5 range = 14—16 days), and the nestling 
period was ~ 15 days (n = 14. range = 13-16 days). 
Each nest was visited at 3- to 5-day intervals 
until either nest failure or Hedging could be 
confirmed. Nest visits were conducted when 
parents were away from their nests to minimize 
the effect of human disturbance. Successful nests 
were defined as those in which at least one chick 
Hedged. Failed nests were classified as: (1) 
depredated if all of the eggs and nestlings 
disappeared before the estimated date of Hedging 
(day 15 after hatching), (2) deserted if all eggs and 
nestlings were found dead in the nest, or (3) 
parasitized by an interspecific brood parasite 
(Common Cuckoo. Cuculits canorus). Daily 
survival rate was estimated using the Mayfield 
Method (Mayfield 1961, 1975: Johnson 1979; 
Klett and Johonson 1982). I calculated daily 
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